低幅度构造特征及其对油气成藏的控制作用: 以鄂尔多斯盆地彭阳地区延安组为例

彭阳地区低幅度构造广泛发育,但由于远离烃源区,油气经历了远距离垂向和侧向运移,导致其对油水分异和与成藏富集的关系不明确。以彭阳地区地质构造演化研究为基础,深入研究了延9层低幅度构造发育特征,结合大量钻井及试采资料,研究了彭阳地区低幅度构造与油气成藏和富集的关系。结果表明,彭阳地区低幅度构造广泛发育,以鼻隆构造为主,构造幅度在18 m以上、闭合面积大于2.8 km²的低幅度构造能够形成有效的油水分异和油气滞留效应,可为油气聚集成藏提供良好的圈闭作用。研究区成藏受古地貌控制,有古地貌坡嘴成藏和河道源头坡度成藏两种古地貌成藏类型,位于古地貌优势成藏区域的低幅度构造易于大面积成藏。彭阳地区低幅度构造可分为10个构造组合单元,其成藏控制因素因所处研究区位置不同而出现差异。东北部(1)—(5)构造组合近生烃中心且位于侏罗系古地貌优势成藏区域,油气主要受构造控制,油气规模随构造幅度和闭合面积的增大而增大;西南部(6)—(10)构造组合单元不在古地貌优势成藏区域,低幅度构造是油气成藏的必要条件而非主控因素,低幅度构造的规模和含油气性也无明显的相关性。

Low-amplitude Structures and Its Control on Hydrocarbon Enrichment and Accumulation: An Example from Yan’an Formation in Pengyang Area,Ordos Basin

Low-amplitude structures are widely developed at Pengyang. As Pengyang is distal from the source rock, the oil had undergone long-distance vertical and lateral migration, and the relations between structures and oil accumulation is unclear. Considering the geological and tectonic characteristics and based on sizable drilling and production data, we studied the low-amplitude structures of Yan 9 oil layer at Pengyang and its controlling effect on hydrocarbon enrichment and accumulation. The results show that low-amplitude structures at Pengyang are widely developed, dominated by nose-like structures. Low-amplitude structures with >18 m structural amplitude and >2.8 km² closed area likely caused effective oil-water heterogeneity, and provided desirable traps for hydrocarbon accumulation. Accumulation of the study area is controlled by paleogeomorphology and can be divided into two types, i.e.slope mouth and fluvial ancient highland slope accumulation. The low-amplitude structures located in the dominant paleogeomorphology accumulation area could facilitate large-scale accumulation, and comprise 10 structural units. As they are in different locations and restricted by different accumulation factors, their hydrocarbon accumulation controlling factors are different. The (1) to (5) structural units in the north are located near the hydrocarbon generation center in the Jurassic paleogeomorphology-dominant accumulation area, with the oil enrichment mainly controlled by the structures. The degree of oil enrichment increases with increasing structural amplitude and closed area. The (6) to (10) structural units in the southwest are not in the Jurassic paleogeomorphology-dominant accumulation area, and low-amplitude structures are necessary for hydrocarbon accumulation (rather than being a main controlling factor). There is no clear correlation between the scale of low-amplitude structures and the degree of oil enrichment.